Cowl structure for a gas turbine engine

ABSTRACT

A cowl structure ( 18 ) for a gas turbine engine ( 10 ) comprises an outer skin ( 26 ) defining a first path for a load applied to the engine ( 10 ). The cowl structure ( 18 ) includes an inner skin ( 24 ) defining a second path for the load. The inner and outer skins ( 24, 26 ) are constructed such that a major proportion of the load is transmitted along the first path.

This application is a division of application Ser. No. 10/361,511, filedFeb. 11, 2003, now U.S. Pat. No. 6,892,526.

FIELD OF THE INVENTION

This invention relates to cowl structures for gas turbine engines.

BACKGROUND OF THE INVENTION

Known gas turbine engines used to power aircraft are subject toasymmetric aerodynamic loads, particularly at the point of take-off ofthe aircraft. Conventionally the nose region of the cowl structuresurrounding the engine is bolted to the engine front flange, and thisresults in these aerodynamic loads being transmitted to the core of theengine and can result in deformation of the engine components.

SUMMARY OF THE INVENTION

According to the present invention there is provided a cowl structurefor a gas turbine engine, the cowl structure comprising inner and outerskins constructed such that at least a major proportion of a loadapplied to the cowl structure is transmitted along the outer skin,wherein the cowl structure has a principal axis and the inner skinincludes first, second and third sections arranged adjacent and in axialalignment with each other parallel to the principal axis of the cowlstructure, the first section being resiliently mounted intermediate thethird and second sections by joint means, the joint means permittingrelative movement between the sections and insulating the second sectionfrom the adjacent cowl structure.

Preferably the outer skin is more rigid than the inner skin. The cowlstructure may further include seal means between the adjacent edges ofsaid first, second and third sections, the seal means extendingsubstantially circumferentially around the inner skin.

The joint means may be flexible to allow said relative movement betweenthe adjacent sections.

In one embodiment the joint means includes bearing means provided on atleast one of the sections, and engagement means extending from theadjacent section to engage the bearing means.

The engagement means may include a plurality of bracket memberssubstantially evenly spaced around and mounted on at least one of thesections.

The joint means may include resilient urging means to allow saidrelative movement between the adjacent sections. The resilient urgingmeans may urge the adjacent sections away from each other.

The resilient urging means may comprise spring means, which extendsubstantially radially outward from the inner skin, to maintainalignment of the internal surfaces. The spring means may comprise aplurality of springs spaced around the cowl structure at regularintervals.

Covering means, which may comprise a projecting member preferablyextends from one of the adjacent sections at the opposite side thereofto the joint means.

Guide means may be provided to guide the first section from a translatedcondition to a non-translated condition.

In the first embodiment where the joint means includes bearing means,the guide means may be provided on the engagement member and may be inthe form of a sloping surface which may be on a leading portion thereofto engage the bearing means as the first and second sections are movedfrom the translated condition to the non-translated condition.

In the second embodiment, where the joint means comprises resilienturging means between the first and second sections, the guide means maycomprise a tapered member extending from the first or second sectionthrough an aperture in the resilient urging means. Preferably, thetapered member extends from the second section through an aperture inthe resilient urging means to releasably secure the resilient urgingmeans to the second section.

The tapered member may comprise an elongate member tapering inwardly atits end remote from the second section. Preferably, the tapered memberis in the form of a dowel.

A door may be provided in the cowl structure to provide access to theinternal components of the engine.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of exampleonly with reference to the accompanying drawings in which:—

FIG. 1 is a diagrammatic, part cross-sectional view of a gas turbineengine;

FIG. 2 is a diagrammatic sectional view of a front part of the engineshown in FIG. 1;

FIG. 3 is a view of one embodiment of the region marked A in FIG. 2;

FIG. 4 is a view of another embodiment of the region marked A in FIG. 2;and

FIG. 5 is a view of the region marked B in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a gas turbine engine 10, having a principal axisX—X, is shown which, in the particular example shown, comprises a core11 having a three shaft configuration (not shown), i.e. a high pressureturbine drives a high pressure compressor via a shaft, an intermediatepressure turbine drives an intermediate stage compressor via a furthershaft, and a low pressure turbine which receives gas flow from theintermediate stage turbine, drives a fan 20 via a further shaft eitherdirectly or through gearing. The high, intermediate and low-pressureturbines, and the high pressure and the intermediate stage compressorare housed within a housing 12 and are not shown in FIG. 1.

The engine 10 is mounted to a wing 14 of an aeroplane via a pylon 16.

The core 11 described above is held within a cowl structure 18 having aprincipal axis aligned with the principal axis X—X of the engine 10. Thefan 20 of the engine draws air into the engine 10. The cowl structure 18extends forwardly of the fan 20 to define a nose region 22 of the cowlstructure 18. The cowl structure 18 comprises an inner skin 24 and anouter skin 26. The inner skin 24 of the cowl structure comprises a firstsection 28 at the nose region 22 (see FIG. 2), and a second section 30arranged downstream of the first section 28 in the direction of air flowthrough the engine 10, along the principal axis X—X of the engine 10. Athird section 32 extends upstream from the first section 28. First jointmeans 34 is provided between the first and second sections 28, 30, andsecond joint means 36 are provided between the first and third sections28, 32.

Referring to FIG. 3, there is shown a first embodiment of the firstjoint means 34 between the first and second sections 28, 30. The firstjoint means 34 shown in FIG. 3 comprises a plurality of discrete bearingmembers 38 provided on the side 40 of the second section 30 facing theouter skin 26. The bearing members 38 are uniformly spaced about thecircumference of the second section 30.

A plurality of uniformly spaced discrete engagement members in the formof brackets 42 are provided on the first section 28 at the edge thereofadjacent the second section 30. The first section 28 being resilientlymounted intermediate the third and second sections 32, 30 by joint means34, the joint means 34 permitting relative movement between the sectionsand insulating the second section 30 from the adjacent cowl structure18. The brackets 42 are provided on the same side of the first section28 as the bearing members 38. Each bracket 42 is aligned with arespective one of the bearing members 38 and projects over the secondsection 30 to slidably engage the bearing member 38.

Covering means in the form of a projecting plate 43, havingsubstantially spherical curvature, is provided on the side 41 of thefirst section 28. The projecting plate 43 extends from the edge of thefirst section 28 to the second section 30 and is received in an indentedportion 45 provided on the second section 30.

The inner skin 24 is, thus, flexibly supported at the adjacent edges ofthe first and second sections 28, 30 at discrete positions around thecowling structure 18. The cowling structure 18 has a projecting memberextending from one of the adjacent sections at the opposite side thereofto the joint means 34.

Seal means in the form of a P-shaped seal 44 is provided in the gapbetween the adjacent edges of the first and second sections 28, 30. Theseal 44 is deformable between a non-deformed condition shown in dottedlines and a deformed condition shown in solid lines. As will bedescribed below, the joint means 36 between the first and third sections28, 32 provides a load on the joint means 34 such that the first andsecond sections 28, 30 are pushed together, thereby deforming the seal44.

In order to carry out maintenance and other work on the engine 10 it isoften necessary to translate the nose region 22 forwardly in thedirection of the arrow F. When this happens, there is some downwarddisplacement by gravity of the nose region 22 relative to the rest ofthe cowling structure 18. When the nose region 22 is translated in thedirection of the arrow G, the first section 28 should be aligned withthe second section 30. To ensure such alignment, each bracket 42 isprovided with a tapered lower leading edge surface 46. When the noseregion 42 is translated in the direction of the arrow G, the surface 46of the bracket 42 slides over the bearing member 40, thereby positioningthe first section 28 in alignment with the second section 30.

Referring to FIG. 4, there is shown an alternative embodiment to thatshown in FIG. 3 in which a plurality of first resilient urging means 48are spaced uniformly around the adjacent edges of the first and secondsections 28, 30. Each first resilient urging means 48 comprises asupport member 50 and a spring member 52. The support member 50 extendssubstantially radially outwardly from the edge of the first section 28and the spring member 52 extends from the free end 54 a of the supportmember 50 to the edge of the second section 30.

A dowel 54 provided at the edge of the second section 30 projectsthrough an aperture 56 in the spring member 52, the dowel 54 beingprovided with a tapering end region 58. When the nose region 22 istranslated in the direction of the arrow F, the spring member 52 isdisengaged from the edge of the second section 30. When this happens, asdescribed above, the nose region 22 drops slightly. However, when thenose region 22 is translated in the opposite direction as indicated bythe arrow G, the edge of the aperture 56 slides over the tapered endregion 58 of the dowel 54 thereby ensuring that the nose region 22 islifted back to its position, as shown in FIG. 4, where the first section28 is aligned with the second section 30.

In each of the embodiments shown in FIGS. 3 and 4, the joint means 34 isflexible and does not allow a pitch or yaw couple on the first section28 to be transmitted to the second section 30. A similar flexibility isprovided at the second joint means 36 between the first section 28 andthe third section 32, as discussed below. In combination, theflexibility between the first and second sections 28 and 30, and betweenthe first and third sections 28 and 32, isolates the second section 30from vertical and side forces originating at or close to the thirdsection 32.

The second joint means 36 (FIG. 5) comprises a plurality of secondresilient urging means 60 substantially uniformly spaced around theadjacent edges of the first and third sections 28, 32. Each secondresilient urging means 60 comprises a support member 62 extendingradially outwardly from the first section 32. The support member 62 isconnected at one end 64 to the third section 32, and a spring member 66is connected to the opposite end region 68 of the support member 62. Thespring member 66 extends between the end region 68 and the edge of thefirst section 28.

Sealing means 70 is provided between the edge of the first section 28and the third section 32. The sealing means 70 is in the form of acircular seal or P-shaped seal, similar to the seal 44 shown in FIGS. 3and 4.

The spring means 60 exerts a force on the section 28 in the directionindicated by the arrow B in FIG. 5, whereby to urge the first section 28towards the second section 30, thereby ensuring that the joint 34retains its integrity.

Thus, the first section 28 of the inner skin 24 is supported at itsopposite ends by respective flexible joints 34, 36. A major proportionof any load applied to the nose region 22 will be transmitted along themore rigid outer skin 26, to the pylon 16 and the wing 14, in preferenceto the inner skin 24. In particular, where the load on the nose region22 is applied upwardly, for example on take off, greater than 90% of theload can be transmitted along the outer skin. This transmission of loadsdirects them away from the core 11 of the engine 10 and avoidsdeformation of engine components within the core 11.

In order to facilitate the transmission of such loads along the outerskin, rigid members are provided between regions of the cowl structurewhere it is necessary to allow access to the fan case mounted engineaccessories. For example, rigid elongate bars may be provided betweenfixed regions of the cowl structure, these bars extending across regionsof the cowl structure that are in the form of doors which can bepivotally opened at a hinge. Alternatively, a slideable region of thecowl structure can replace the door structure. In such cases, theslideable regions may themselves be sufficiently rigid to allow saidload to be transmitted there along. A further alternative is theprovision of rigid doors within a fixed cowl to provide access to fancase mounted engine accessories.

Various modifications can be made without departing from the scope ofthe invention. For example, the inner skin may be constructed so thatthe entire load applied upwardly on the nose region 22 on takeoff istransmitted along the outer skin.

Whilst the present invention has been described with reference to thenose region 22 of the cowl structure 18 which extends forward of the fan20, it will be appreciated by one skilled in the art that it is equallyapplicable to other sections of the cowl structure 18. For example theinvention could be used in the region of the cowl structure 18downstream of the engine 10, which forms the exhaust nozzle.

The present invention is of particular benefit in high-speedapplications where there is a need to minimise steps and gaps in theouter skin 26 of the cowl structure 18 for aerodynamic purposes.

1. A cowl structure for a gas turbine engine, the cowl structurecomprising inner and outer skins constructed such that at least a majorproportion of a load applied to the cowl structure is transmitted alongthe outer skin, wherein the cowl structure has a principal axis and theinner skin includes first, second and third sections arranged adjacentand in axial alignment with each other parallel to the principal axis ofthe cowl structure, the first section being resiliently mountedintermediate the second and third sections by joint means, the jointmeans permitting relative movement between the sections and insulatingthe second section from the adjacent cowl structure, the joint meansincludes resilient urging means to allow said relative movement betweenthe sections and urge the adjacent sections away from each other whereinthe resilient urging means comprises spring means wherein the cowlstructure further comprises internal surfaces across which air can passin use, wherein the spring means extends substantially radiallyoutwardly from the inner skin, to maintain alignment of the internalsurfaces.
 2. A cowl structure for a gas turbine engine, the cowlstructure comprising inner and outer skins constructed such that atleast a major proportion of a load applied to the cowl structure istransmitted along the outer skin, wherein the cowl structure has aprincipal axis and the inner skin includes first, second and thirdsections arranged adjacent and in axial alignment with each otherparallel to the principal axis of the cowl structure, the first sectionbeing resiliently mounted intermediate the second and third sections byjoint means, the joint means permitting relative movement between thesections and insulating the second section from the adjacent cowlstructure, the joint means including resilient urging means to allowsaid relative movement between the sections and to urge the adjacentsections away from each other wherein the resilient urging meanscomprises spring means and wherein the spring means comprises aplurality of spring members spaced around the cowl structure atsubstantially regular intervals.